In 1970 on the world’s first Earth Day, leading ecologist, Dr Barry Commoner, laid out the four basic rules for human’s relationship to the environment. One of them was that there’s no such thing as a free lunch.

I flashback to this day the more I read about the wondrous advantages of vertical, indoor farming. While a simple Google search reveals incredible conceptual drawings, it is harder to find analysis of its environmental and economic costs.

In a recorded seminar, Dr Louis Albright, the emeritus professor of biological and environmental engineering at Cornell University, uses wheat, lettuce and tomatoes to look at the issue of producing crops in enclosed spaces in terms of kilowatts of energy, moles of light, growth per square metre and kilograms of CO2 released.

Some of the numbers below are updated from what you will see in the seminar; received via personal communication with Albright. Like him, I will also use New York City (with its population of 8.6 million in 2013) to examine the practicalities.

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Wheat

New York City residents each consumed about 24kg of bread per year. It would take about 8.6m square metres of floor space stacked three high per floor, to grow New York City’s wheat. That’s equal to nearly three Empire State Buildings. It might seem very efficient to produce all the bread in three large buildings, but constructing and running them will have their own environmental footprint.

Assuming the use of efficient red-blue LEDs at $0.10 per kilowatt-hour, production alone would cost about $327 (£223) per square metre per year. If turned into bread it would cost $11 per loaf of bread to cover the lighting cost.

Lettuce and tomatoes

Maybe lettuce and tomatoes are a better bet. Albright analysed two systems – one with 100% indoor light versus one with 30% indoor light and 70% solar capture (representative of a greenhouse with supplemental light).

One claim for fully lit, indoor systems is a reduction in the food’s carbon footprint. With 100% supplemental light Albright’s analysis shows about 3.95kg of CO2 is produced per kg of head lettuce. The average US passenger car emits about 5,100 kg of CO2 per year – so the production of 8,300 heads of lettuce in this system is equivalent to one year’s car travel.

What’s more, the full indoor light system would use about 1,000 kWh per square metre each year, costing $0.10 per head for light electricity. This puts a pretty high baseline on the head lettuce market price.

For tomatoes, the average US resident consumes about 8.2kg annually. With the CO2 cost at 8.7kg per kg of tomato, we’re looking at the CO2 equivalent of 264,000 US passenger cars.

Is there another way?

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As part of improving sustainability and resilience, city region food systems in the developed world need to be strengthened and food should be sourced, on average, closer to home. However, does it makes sense to put a lot of intellectual activity and resources into something that negates the direct use of our one absolutely renewable resource – the sun – and replace it with artificial light? Aren’t there other strategies for moving production closer to home?

Perhaps its time we moved beyond 100% artificial lighting to consider other possibilities, such as field level tunnels that keep crops from frost kill in the early spring and late fall; unheated high tunnels that use only solar capture to produce crops year-round in colder climates; and greenhouses with heat and supplemental light for a full 12-month production of a wider range of crops.

In a 2008 study on crop product flown into New York, the authors found that transporting lettuce across the US produced 0.70 kg of CO2 per kg. Yet, according to Albright’s calculations, 100% artificially lit systems would produce about 3.95kg of CO2 per kg lettuce for the lighting – more than five times greater.

I am unable to find evidence that 100% artificially lit systems are the answer to feeding cities sustainably. The environmental cost (judged only by carbon footprint in this case) is clearly higher than other strategies.

A better use of time, resources, and capital with greater potential for long-term impact is continued development of controlled to semi-controlled environments with the sun as the basis of production.

Greenhouses or unheated hoophouses can be sited in urban areas on abandoned land or rooftops and in the surrounding peri-urban and near-rural areas. In higher latitudes, these types of growing environments allow land-use over the full year – a form of sustainable intensification for city regions.

They have real potential to help supply a healthy diet in city regions across the globe and to help insure sustainable livelihoods for a diversity of farmers in city regions. This is clearly not the case for 100% artificially lit systems.